Power semiconductor modules may comprise a power inverter or a converter and generally at least one power semiconductor chip or a power semiconductor component. The latter may control and switch high electrical currents and voltages. Such a power semiconductor component may include a power metal-oxide field effect transistor (power MOSFET), a power diode, or a bipolar transistor with an insulated gate electrode (insulated-gate bipolar transistor, abbreviated to IGBT). To form the power semiconductor module, the power semiconductor components are usually soldered onto a substrate and connected to each other electrically by bond connections.
Power semiconductor modules can be characterized by an expected lifetime. The lifetime corresponds to the time until the power semiconductor module fails or becomes functionally non-viable. During operation of the power semiconductor module a remaining lifetime of the power semiconductor module can change through a deterioration of the power semiconductor module, for example. In particular, the remaining lifetime of the power semiconductor module reduces if the power module deteriorates.
The deterioration of the power semiconductor module may be accelerated during any operation in which the power semiconductor modules is subjected to thermal and mechanical stresses. These stresses can lead to a so-called thermomechanical fatigue of the power semiconductor module, which may result in the failure or a functional non-viability of the power semiconductor module (e.g., the end of the lifetime). Thermal stresses may include temperature change stresses from the electrical operation of the power semiconductor module as a result of different coefficients of thermal expansion of the materials in the power semiconductor module. Such examples may include fatigue at the electrical connection points, for example of bond connections and solder connections of the chip solder and of the system solder. The fatigue at the connection points may cause the bond connections or the solder connections to work loose, which leads to an increased temperature of the semiconductor chip. Thus the thermomechanical fatigue of the power semiconductor module causes the deterioration of the power semiconductor module to accelerate, which can lead to a reduced remaining lifetime and to a premature failure of the power semiconductor module.
To guarantee safe operation of the power semiconductor module, some systems use a prediction of the lifetime of the power semiconductor module. In the prior art, lifetime calculations may be based on lifetime curves and predetermined load profiles, and carried out with computer support. For this purpose, for example a temperature of the power semiconductor modules is monitored. In some systems, thermistors are soldered to the substrate along with the power semiconductor components. The spatial separation of the thermistors from the power semiconductor components inhibits the detectiong of exact transient temperatures of the chips, and reduces the accuracy of the lifetime calculations.
In some systems, equivalent thermal networks are created for the power semiconductor modules, on the basis of which conclusions can be drawn indirectly about the temperature of power semiconductor components. The electrical losses of the IGBTs and of the diodes can be calculated from current and voltage measurements or using the knowledge of the operating point of the power semiconductor module. Thus, although the temperatures of the power semiconductor components during operation can be calculated, no account is generally taken in the equivalent thermal networks of any deterioration of the power semiconductor components.
The teachings of the present disclosure may provide a solution through which a deterioration of power semiconductor modules can be determined more reliably and through this solution a remaining lifetime of the power semiconductor modules can be predicted more accurately. For example, some embodiments may include a method for characterizing a power semiconductor module comprising: determining a thermal model (4) of a power semiconductor module (1) at a reference time point; establishing a reference temperature (Tj,zth) on the basis of the thermal model (4) of the power semiconductor module (1); measuring at least one temperature-sensitive electrical parameter (TSEP) of the power semiconductor module (1) at at least one later point in time compared to the reference time point, during operation of the power semiconductor module (1); establishing a current temperature (Tj,tsep) of the power semiconductor module (1) from the at least one measured temperature-sensitive electrical parameter (TSEP) of the power semiconductor module (1); establishing a temperature difference (ΔT) between the current temperature (Tj,tsep) and the reference temperature (Tj,zth); and determining a deterioration of the power semiconductor module (1) on the basis of the temperature difference (ΔT) established.
In some embodiments, for creation of the thermal model (4), a thermal impedance of the power semiconductor module (1) describing a thermal path of the power semiconductor module (1) is determined.
In some embodiments, for creation of the thermal model (4), a power dissipation (P) of the power semiconductor module (1) is determined.
In some embodiments, for creation of the thermal model (4), a temperature (Tc) of a cooling element (3) of the power semiconductor module (1) is acquired during operation of the power semiconductor module (1).
In some embodiments, a power semiconductor module (1) is characterized, which has a IGBT as the at least one power semiconductor component (2).
In some embodiments, an electrical threshold voltage and/or a Miller plateau and/or a turn-on delay time and/or a turn-off delay time and/or a maximum speed of current increase (dI/dt|max) and/or a recovered charge and/or a tail current and/or a voltage peak UEE′max) during a turn-on process and/or a turn-on duration and/or a turn-off duration is measured as the at least one temperature-sensitive electrical parameter (TSEP).
In some embodiments, a characteristic curve (6) is determined, on the basis of which each value of the at least one temperature-sensitive electrical parameter (TSEP) is assigned a temperature value, wherein one of the temperature values is determined as a function of the measured temperature-sensitive electrical parameter (TSEP) as the current temperature (Tj,tsep).
In some embodiments, for determining the characteristic curve (6), the temperature values are predetermined for the power semiconductor module (1), the power semiconductor module (1) is set to the respective temperature value and the respective value of the at least one temperature-sensitive electrical parameter (TSEP) is measured at the predetermined temperature value.
In some embodiments, a heating device is provided for setting the temperature values, by means of which a temperature of the power semiconductor module (1) is increased step-by-step to the respective predetermined temperature values.
In some embodiments, the measurement of the at least one temperature-sensitive electrical parameter (TSEP) for creating the characteristic curve (6) is carried out at the respective predetermined temperature value by means of a double-pulse measurement circuit (10).
As another example, some embodiments may include a device for characterizing a power semiconductor module (1) during operation of the power semiconductor module (1). The device may include a measuring device for measuring at least one temperature-sensitive electrical parameter (TSEP) of the power semiconductor module (1) and a calculation device for establishing a current temperature (Tj,tsep) from the at least one temperature-sensitive electrical parameter (TSEP) and for calculating a temperature difference (ΔT) between a predetermined reference temperature (Tj,zth) and the current temperature (Tj,tsep).
As another example, some embodiments, may include a circuit arrangement, which has a power semiconductor module (1) with at least one power semiconductor component (2) and a device as described above.
In some embodiments, the power semiconductor module (1) comprises an inverter and at least one cooling element (3), wherein the inverter has at least one IGBT as the at least one power semiconductor component (2).
In some embodiments, the circuit arrangement has a control device (7), which is designed to regulate a power of the power semiconductor module (2) as a function of the temperature difference (ΔT) established.